1. Field of the Invention
The present invention relates to a sheet coil type resolver which uses a sheet coil as its electric conductor.
2. Description of the Related Art
A conventional sheet coil type resolver is disclosed and includes: an excitation coil of a single phase which is formed of a flat sheet coil such that the angle of each pole of pole-pair number X is 180 degrees in electrical angle; and a detection coil of two phases (phases A and B) which is formed of a flat sheet coil and disposed to axially oppose the excitation coil with a gap distance therebetween wherein phases A and B have a phase difference of 90 degrees in electrical angle from each other (refer to Japanese Patent Application Laid-Open No. H8-136211).
FIG. 14 shows schematically a radial cross section of a rotor coil system at a rotor section of a conventional sheet coil type resolver. In the rotor coil system at the rotor section, a resolver coil 1005 as an excitation coil is disposed at a radially outer side of a circular disk shaped insulation sheet 1004, and a transformer coil (secondary winding) 1006 to supply an excitation current to the resolver coil (excitation coil) 1005 is disposed at a radially inner side of the insulation sheet 1004 so as to be located radially inward of the resolver coil (excitation coil) 1005 thus located close to a rotary shaft. The aforementioned two coils 1005 and 1006 are disposed to face a circular disk-shaped rotor core.
On the other hand, a stator coil system of a stator section of the sheet coil type resolver, though not shown, includes a resolver coil (as a detection coil) having a two-layer structure composed of A- and B-phase detection coils and a transformer coil (primary coil) and is arranged in the same way as the rotor coil system, specifically such that the transformer coil (primary coil) is disposed radially inward of the resolver coil (detection coil).
A transformer coil system is constituted such that the transformer coil (secondary winding) at the rotor section and the transformer coil (primary winding) at the stator section are disposed to axially oppose each other. Also, a resolver coil system is constituted such that the excitation coil at the rotor section and the detection coil composed of the A- and B-phase detection coils at the stator section are disposed to axially oppose each other.
The sheet coil type resolver disclosed in Japanese Patent Application Laid-Open No. H8-136211, however, has the following defects. The transformer coil (secondary winding) of the rotor section is disposed radially inward of the excitation coil and located close to the rotary shaft, and the transformer coil (primary winding) of the stator section is disposed radially inward of the detection coil and located close to the rotary shaft. Thus, in the above described coil arrangement at each of the rotor section and the stator section, two kinds of coils are disposed concentrically to each other on one plane with one coil located radially outward of the other coil located close to the rotary shaft, and therefore both the rotor section and the stator section are forced to have an enlarged diameter thus making downsizing difficult. Also, the rotor core and the stator core are inevitably forced to have an enlarged diameter, too, and therefore apt to suffer distortion in shape.
Further, since the distance is large between the rotary shaft and the outer circumference of the resolver, the centrifugal force is easily generated and accordingly the area between the rotary shaft and the rotor core is susceptible to stress concentration. Consequently, it is possible that the rotor section and the rotary shaft are shifted from each other and also that the joint area therebetween is fractured.
Moreover, terminals of the transformer coil disposed radially inwardly need to be led out outside at the stator section, and in order to secure the space for leading out the terminals, the space which is allocated for the resolver coil disposed radially outwardly must be diminished or an additional layer for a wiring of the lead wires must be provided.